Synthesis of Al-rich ZSM-12 using TEAOH as template

Abstract

Hydrothermal synthesis of ZSM-12 (MTW) with tetraethylammonium hydroxide (TEAOH) as template was systematically studied with the objective of obtaining an aluminum rich zeolite. In contrast to other zeolites, published information on the synthesis of ZSM-12, especially aluminum rich samples, is limited since its preparation is a difficult task due to its inherent high silica character. The effect of aluminum content of the gel, the OH(-)/SiO(2) ratio and the TEA/SiO(2) ratio were examined and the crystallization domain of pure ZSM-12 phase was identified as a function of these parameters. TEA/SiO(2) and OH-/SiO2 ratios much lower than what is typically used in zeolite synthesis were found to be favorable for crystallization of ZSM-12, especially at Si/Al ratios ranging from 30 to 50. In this study, we were able to successfully synthesize ZSM-12 with Si/Al ratio of 31. This was achieved from gels having TEA/SiO(2) ratios of 0.125 as well as 0.16 and OH(-)/SiO(2) ratio of 0.07. The products obtained were characterized by XRD, SEM, BET and TGA. The results clearly showed that pure ZSM-12 with high crystallinity was obtained in all the batches. The amount of organic retained in the zeolites after synthesis was constant but the state of TEA was very different depending on the Si/Al ratio of the zeolite. (C) 2001 Elsevier Science B.V. All rights reserved.